JSFiddle - React, Tailwind, and code Playground
HTML
<script id="preloadInsert">test: function(){var newP = document.createElement("p"); newP.innerHTML = "Just test"; document.body.appendHTML(newP)}</script>
JavaScript
// Запускаем код до готовности DOM или после
test();
document.body.removeChild( document.getElementById("preloadInsert") );